Just lost quality of cut even with sharp blades- Help!

I bought a 21" Honda Harmony a couple months ago and at the time it cut great. After the blades dulled a little, the quality of cut got worse, to the point where there would be rows of partially-cut grass leftover from overlapping the mowing path. I bought new blades and a bench grinder and sharpened them all. The cut didn't improve- even with very sharp blades (I did dip the blades in water often while grinding to keep the blade temper), and overlapping a lot while mowing (so the deck goes over the wheel tracks), and with dry St. Augustine grass, not only are there errant blades that are untouched after going under the deck, but around the edges of each mowing path, there are semi-cut paths of grass, whole ROWS of uncut grass! In other words, the mower is cutting the grass in these rows but it's a noticeable inch or so higher than the rest of the cut grass. The underside of the deck is clean, deck height set as usual, and I'm mowing properties poorly now that I've mowed when the Honda was brand-new that looked great then. I'm dumbfounded.. searching the forums didn't turn up much info. Has anyone experienced this or have a suggestion? The grass that is cut well looks like it was cut with a scissors, so I know the blades are sharp.. but something is very wrong. I'm not going to change mowers anytime soon since this is a small business I'm running while in college and the Honda was $500.. and it used to cut perfectly!

Checked the deck and it's clean.. the Harmony uses twin blades and they're installed correctly.. all wheels are set to the same height.. engine speed is as it's always been based on the sound pitch.. ground speed is the same when I mow.. all variables I can think of so far are the same as when the mower would cut well. I appreciate the suggestion though, of course.

We had a HRC21 that wasnt cutting good like the others we have. It was not right from when it was new. We took it to the dealer several times, and they would always say they couldnt find any problem. It would bog down some times and left a crappy cut. Well the mechanic finally pulled the engine apart and checked the govenor. It had a broken tab on one side of the weight that makes the gov. kick in and it was sticking and not reacting to engine load. It was a $6 part that was probably bad from the factory. All fixed and cuts like a champ, just like the other 4 we have. :blob1: